In the Japanese version, Professor Fungi is constantly seen smoking a pipe. It was removed in the international releases.
In the Japanese version, the guns in the Western Land ending cutscene are revolvers. They were changed to Yellow Cork Shooters in the international release.
This is the first (and currently only) game in the Mario Party series where the characters' costumes change based on the board being played.
Contributed by RyuHane
The game contains unused text that says:

You cannot use a Bowser Bomb here.
Contributed by MeleeWaluigi